DE60023743T2 - CATALYST WITH HIGH RESISTANCE AND LARGE SURFACE, CATALYST SUPPORT OR ADSORBER COMPOUNDS - Google Patents

Description

The This application takes priority of the US Provisional Application No. No. 60 / 173,592 filed on December 29, 1999, entitled "High Strength and High Surface Area Catalyst, Catalyst Support or Adsorber Compositions "by Wu et al Claim.

Background of the invention

1. Field of the invention

The The present invention relates to an improved zeolite / silica / alumina material and a Process for producing such a material. It concerns in particular a zeolite / silica / alumina composite material, which has excellent strength and large surface area.

2. Background and discussion of the prior art

The "Clean Air Act" of 1970 requires that a catalytic converter is installed in an automobile to control the exhaust gas flow to clean. The catalyst removes unburned fuel, Carbon monoxide and nitrogen oxides simultaneously in the exhaust stream. A conventional one Catalyst consists of a multi-channel ceramic honeycomb structure and close a material with a big one surface one, that is along with the actual catalytic Material (for example, the three-way catalyst (TWC)), the on the ceramic material is applied by washcoating. The monolithic ceramic honeycomb provides a strong substrate for the catalyst ready and fulfilled additionally mechanical and thermal requirements. As it is, however, as inert Structure does not take the catalyst substrate to the chemical Reactions for the removal of unburned hydrocarbons, Carbon monoxide and nitrogen oxides in part.

US Patent No. Re. 34,804 discloses the formation of extruded zeolite honeycomb bodies include a silicone resin component as a permanent binder. One improved process for the preparation of the zeolite body is in U.S. Patent No. 5,492,883 (Wu), wherein the zeolite material with an aqueous Silicone resin emulsion and a temporary binder such as Methylcellulose is mixed and the mixture to form a unfired honeycomb body is extruded, which is then dried and sintered. Another one improved process for producing a zeolite body is in U.S. Patent No. 5,633,217 (Lynn), which discloses the use a dibasic ester as a solvent for the silicone resin and the use of a temporary Methylcellulose binder disclosed. Recently disclosed US Patent No. 5,565,394 (Lachman et al.) Improved zeolite bodies, which a thermal expansion control component such as calcium silicate, a permanent binder such as For example, silica or alumina and a temporary binder such as methylcellulose. Although the zeolites, the are not disclosed in the documents of Wu, Lynn and Lachman are inert and are capable of being used as a catalyst material These require the use of an expensive metal washcoat, respectively (washcoating) to operate as a three-way catalyst, the for the conversion of hydrocarbons, nitrogen oxides and carbon monoxide in their non-toxic gaseous counterparts be able to.

For zeolite-based Materials used as monolithic honeycomb structures at elevated temperatures (> 300 ° C) used The zeolite material should be the following combination have properties that conventional zeolite bodies do not have: high strength, large Surface, size thermal stability (i.e., high thermal shock resistance) and low coefficient of thermal expansion. There is accordingly a clearer Need for a zeolite material that needed the previously mentioned Properties shows and it is thus an object of the present Invention, a zeolite material to provide accordingly.

Summary the invention

The The object of the present invention is to solve the above problems to solve the prior art and to provide a zeolite material with high strength and high surface area, that a great thermal stability and low thermal expansion shows.

In particular, the present invention is directed to a zeolite body comprising, in terms of weight percent, the following:
30-70% zeolite with a silica / alumina ratio of at least 300 and a surface area greater than about 250 m ² / g, 15-20% silica binder and 10-50% gamma-alumina having a specific surface area greater than 100 m ² / g. The properties of this zeolite based material include: (1) a modulus of rupture of at least 1406138 kg / m ² (2000 psi); (2) a surface area of at least 100 m ² / g; (3) a thermal expansion coefficient of less than about +/- 10 ppm / ° C; and (4) a thermal shock resistance of at least 850 ° C.

Full Description of the invention

The product of the present invention is a zeolite body for use as an adsorbent or catalyst support, particularly a zeolite-based material, wherein the zeolite has a silica to alumina ratio of at least greater than 300 and a surface area of at least 250 ^m2 / g. Expressed in parts by weight, the zeolite-based bodies according to the present invention typically contain between about 30-70 parts by weight of zeolite and 15-20 parts by weight of silica binder.

Typically, zeolites include large particles on the order of several micrometers and exhibit a regular array of accessible micropores, a combination that provides the feature of the large surface area of zeolites; a feature that is retained by the zeolites even after sintering. In general, such catalyst support and adsorber applications require substantially total surface areas of at least 20 m ² / g, preferably greater than 100 m ² / g, and most preferably greater than 150-200 m ² / g. The zeolite-based body of the present invention is capable of being extruded into a thin-walled, high cell density monolithic body, such as a honeycomb structure having at least 400 cells / in ² , a surface area of at least 200 m ² / g 250 m ² / g are easily accessible.

As described in detail above, the zeolite constituent is desirably a high silica-containing zeolite having a SiO ₂ / Al ₂ O ₃ mole ratio of at least 300. The presence of the high silica / alumina ratio zeolite provides a zeolite-based material with both thermal stability at such high temperatures typically expected in the vicinity of exhaust gases and the expected ability to adsorb and desorb hydrocarbons , ready. In other words, the high silica content of the zeolite provides a composite with the ability to maintain its structure at high temperatures. On the other hand, the presence of a low alumina content in the zeolite ensures that the zeolite will not experience the type of moisture problems typically associated with high alumina zeolites; High alumina zeolites typically dealaubum in the presence of moisture at high temperatures. In addition, the zeolite crystal silica phase is maintained at high temperatures and is responsible for the negative CTI (coefficient of thermal expansion) which acts as a balancing agent so as to reduce the overall thermal expansion of the composite. In summary, the material of the present invention provides a zeolite adsorbent material that allows the designer of automotive exhaust systems a degree of flexibility in the design of the exhaust system; the adsorbent material has increased thermal stability.

suitable Close zeolites any silica-based zeolites that are the prerequisite a very high silica / alumina ratio fulfill. Useful zeolites containing a high silica to alumina ratio for the exercise of the invention can be found among the zeolites, which are from the following selected are: mordenite, ultrastabilized Y (USY), ZSM-5, ZSM-8, ZSM-11, ZSM-12, Hyper Y, Beta Zeolites, H-Ferrierite, H-Offretite, Faujasite, X zeolite, type L zeolite, mazzitol, EMC-2 and combinations of these, preferably silicalite and any of the natural zeolites, the erionite, Clinoptilolite, chanazite and phillipsite. A commercially available zeolite with the necessary silica rich properties is CBV 3002, available from the PQ Corporation.

In addition to a large surface area, other features of this zeolite body which make it suitable for use as an adsorbent material include its relatively high thermal expansion and high thermal stability; less than 10 ppm / ° C, preferably 5 ppm / ° C, and thermal stability of up to at least 1000 ° C each. In addition, catalyst support applications and filter / adsorber applications preferably require flexural fracture toughness in excess of 1500 psi. The zeolite body of the present invention exhibits flexural and compressive strengths that exceed this value and are larger in the order of as 1406138 kg / m ² (2000 psi) wherein MORs are accessible (psi 3500) to a value of 2460743 kg / m ² ,

A second embodiment of the zeolite body according to the invention comprises the inclusion of a third component, a gamma-alumina, having a surface area greater than 100 m ² / g. The high surface area gamma alumina component also helps to have an overall zeolite-based body that is within the surface requirements of many catalyst support applications. Expressed in parts by weight, the zeolite / silica / alumina bodies of the invention characteristically contain between about 30-70 parts by weight of zeolite and 15-20 parts by weight of silica binder and 10-50 parts by weight of gamma-alumina.

Even though the presence of silica the incorporation of PGM catalysts into the extruded zeolite substrate due to the known PGM incompatibility of the silica prevents the presence of aluminum oxide in this embodiment the zeolite-based composite structure the support material function for non-PGM catalysts ready. In particular, gamma-alumina sees the necessary places prior to binding of a transition metal oxide catalyst to enable the structure such that the composite material has improved catalytic activity and lifetime across from only on zeolite-based structures will show if it is in certain rough environments is used, which is typically high Temperature are connected, and as for example in chemical Processing applications are seen. In addition, the alumina, wherein the transition metal oxides typically arranged, porous enough and showing sufficient size surface with porous Structure to prevent sintering of the metal oxides that are present and accessibility the transition metal oxides across from to provide the reactant stream.

Gamma alumina suitable for use in the formation of this composite material is close such aluminas, which after calcining the required Provide gamma-alumina phase and show a sufficiently large surface, sufficient to serve as a catalyst carrier material. One suitable commercially available Gamma-alumina with the required high surface characteristic is GL-25, which can be obtained from LaRoche Industries.

In another embodiment, the zeolite body should include a stabilized large surface area alumina. The stabilized alumina should include an amount of stabilizer selected from the group consisting of lanthana (La ₂ O ₃ ) or its equivalents, including barium oxide, strontium oxide and yttria. These stabilizers are known to stabilize the specific surface area of the alumina, which in its pure form is typically unstable at high temperatures. In particular, the stabilizers inhibit the phase transformation of alumina at high temperatures and thereby increase the stability of the alumina at high temperatures. The stabilizers are typically included in the alumina as a pre-dopant prior to the batch formation of the composite and are preferably added to the composite after firing via an impregnation process.

A preferred stabilizer for alumina is lanthanum oxide (La ₂ O ₃ ), which is impregnated into the gamma-alumina component of the composite. The lanthanum impregnation is carried out such that the composition contains lanthanum oxide in the weight range of 0.5-20 parts by weight with respect to the alumina component amount. When lanthanum is added in a smaller amount than in such a range, the beneficial effects of increasing activity due to the lanthanum addition are no longer observed.

For catalyst applications should the porosity measured as total porosity of the zeolite / alumina composition to be sufficient Access to the transition metal oxide catalyst through the walls to enable. For adsorber applications should the porosity measured by the average pore size to be sufficient support function to enable to effectively serve as adsorber. The selection range for total porosity and average Pore size can be varied to the proposed catalyst or adsorber applications take. The porosity depends on from the starting materials and the firing temperature, the higher the Temperature the denser the resulting structure. For catalyst and / or catalyst carrier applications can the zeolite structures according to the invention a total porosity of about at least 30% along with average sub-micron pore sizes exhibit.

In addition to its use as a simple adsorber structure as stated above the silica-rich / alumina zeolite material of the present invention be used as a catalyst substrate, in particular as a replacement for cordierite. Alternatively, the zeolite of the invention may be used as catalyst substrate be used in such applications where there is the additional Function of the adsorption of hydrocarbons during the Cold start stage (for example Bag I and II emissions).

In The first catalyst substrate embodiment becomes the zeolite honeycomb substrate washcoating with a conventional three way catalyst subjected and the catalyst system works in the same way like a regular one Cordierite-based Three-way catalyst system. Suitable catalytic materials for Superimposed on the silica-rich / alumina zeolite substrate shut down Platinum, palladium, rhodium and iridium. The zeolite substrate consists of a zeolite material that provides high thermal stability Automotive exhaust conditions shows. Suitable zeolites include those selected from the following materials: mordenite, ultrastabilized Y (USY), ZSM-5, ZSM-8, ZSM-11, ZSM-12, all of which have a silica / alumina ratio of 300 and above demonstrate.

In the second embodiment For example, the zeolite substrate is washcoated with an oxidation catalyst subject; suitable oxidation catalysts include platinum, Palladium, rhodium or iridium. The washcoated Zeolite catalyst serves as a hydrocarbon trap for the reduction of Hydrocarbon emissions during the cold-start stage. The zeolite material selection for the substrate includes Beta zeolite, USY and ZSM-5 and mordenite, all the required high silica / alumina ratio of 300 or above demonstrate. These large pores Zeolites show a big one ability for the adsorption of hydrocarbons while at the same time show required thermal stability, to survive the harsh environment in an automotive exhaust flow. When the washcoated catalytic oxidation material If sufficient material is reached it serves to destroy dangerous ones Hydrocarbon molecules by oxidizing these molecules with oxygen, which is present in the automotive exhaust stream, too environmentally friendly molecules for example, water and carbon dioxide.

The general process for the production of porous sintered substrates takes place as the expert knows, done by mixing the batch materials, mixing the mixture, forming a reclaimed or green body or Molding and subsequent Sintering the unfired body to a hard porous structure. In this type of preparation of the body are different lubricants such as zinc stearate and sodium stearate and organic Binder the approach during added to the mixing step for viscosity control and strength provide before firing and a porosity for the structure after firing.

A particularly preferred method of making the composition of the invention described herein, an extruded high surface area honeycomb monolith, comprises blending certain starting materials into a substantially homogeneous body which is capable of forming the above-mentioned composition , In particular, the starting materials that will form a composition will include a zeolite starting material, the m, a silica / alumina ratio of at least 300 to 1 and a surface area of at least 250 ² / g, a silica binder comprising a resin / solvent ratio of between 2/1 to 4/1 and optionally a gamma alumina component having a specific surface area greater than 100 m ² / g. As is standard in the formation of ceramic structures, the batch mixture should include a temporary organic binder and water. The preferred method of forming the body involves extruding the body to form an unfired honeycomb structure. Once formed into a honeycomb body, the extruded green body is then dried by heating the structure for a time sufficient to form a crack-free dry structure. The drying step is achieved in many different ways. One embodiment includes placing the structure in an oven at a temperature in the range of 50-100 ° C, preferably at a temperature in the range of 90-100 ° C for periods of up to four days. In another slightly modified embodiment, the drying step is achieved by placing the greenware in a controlled oven at relative humidity (e.g., 90% relative humidity) for similar times and temperatures as the aforementioned standard oven-drying embodiment. In a third embodiment, the drying step is accomplished by placing the greenware in a dielectric oven for a time sufficient to form a crack-free self-supporting structure, preferably a period of not more than 60 minutes, more preferably a period of 5-30 minutes.

Sintering the dried honeycomb structure involves heating or sintering the honeycomb for a time sufficient to form a sintered structure having a high surface area. In particular, the sintering comprises heating the honeycomb in a nitrogen atmosphere at a rate of 10-25 ° C / hr. to a first temperature of at least 500 ° C, this temperature is then preferably maintained for a period of up to 10 hours, more preferably 4 hours. Following nitrogen pretreatment and firing, the honeycomb is cooled to ambient temperature. When ambient temperature is reached, the honeycomb is heated in air to a second temperature of at least 850 ° C, preferably 1100 ° C. The second air heating step to at least 850 ° C can be two different heating steps including: (1) a first heating step at a speed of 10-25 ° C / hr. to 500 ° C after which the temperature is maintained for a period of time; and (2) a second heating step from 500 ° C to at least 850 ° C at a rate of about 50 ° C / hr. after which the temperature is again maintained for a period of time. For both air heating steps, the holding temperature is preferably maintained for a period of up to 10 hours, more preferably 4 hours.

Of the Pretreatment nitrogen heating step will presumably have sintered structures the result, the one opposite such bodies increased MOR that were not rejected this pretreatment step. Without wishing to be bound by theory, it is believed that the nitrogen pretreatment a gradual slow burning out The organic binder does not create the microstructure of the zeolite body disturbs, and thus easier compaction of the zeolite body the later reached higher Burning temperatures allows.

The purpose of the organic binder is to provide plasticity and some green strength after drying during molding. An organic binder according to the present invention relates to cellulose ether type binders and / or their derivatives, some of which are thermally gellable. Some typical organic binders according to the present invention are methyl cellulose, hydroxybutyl cellulose, hydrobutyl cellulose, hydroxyethyl cellulose, hydroxymethyl cellulose, hydroxypropyl cellulose, hydroxypropylmethyl cellulose, hydroxyethylmethyl cellulose, sodium carboxymethyl cellulose and mixtures thereof. Methylcellulose and / or methylcellulose derivatives are typically used in the practice of the present invention. Methylcellulose, hydroxypropylmethylcellulose and combinations thereof are particularly preferred. Preferred sources of cellulose ethers and / or derivatives thereof are Methocel A4M, F4M and F240M from Dow Chemical Corporation. Methocel A4M is a methylcellulose binder with a gel temperature of 50-55 ° C and a gel strength of 5000 g / cm ² (based on a 2% solution at 65 ° C). Methocel F4M and F240M are hydroxypropyl methylcellulose.

Examples

Around to further illustrate the principles of the present invention certain examples of zeolite and zeolite / alumina bodies are described be that according to the invention are formed, as well as a comparison body. It should be clear, however be that the examples are given for comparative purposes only and the invention is not limited thereto but much more different Modifications and changes can be made in the invention without the spirit and scope to deviate from the invention.

Examples 1 and 2

Both examples involved careful mixing of a batch mix as indicated in Table I in a Littleford mixer. The zeolite raw material comprised a ZSM-5 zeolite having a SiO ₂ / Al ₂ O ₃ ratio of 300 (CBV-3002 from PQ Corporation) and a silica binder containing an amount of concentrated silicone resin (6-2230 resin from Dow Coming) dissolved in a dibasic ester solution having the resin-solvent ratio shown in the table; In each example, the amount of resin resulted in an amount of permanent silica binder recorded for the fired composition. The mixed batch was transferred to a grinding roll and an amount of water as indicated in Table I was added to the batch and the batch was uniformly plasticized; the water listed as the additional additive is given in weight percent based on the fired composition.

The honeycomb bodies having a wall thickness of about 8 mils, having 400 cells / in ² , and bars suitable for testing the MOR and having a diameter of 0.3125 inches were formed by extrusion through a piston extruder. Each of the two examples, the green extruded honeycombs and the rods were dried in the following manner: room temperature to 95 ° C in a humidity oven (95-100% relative humidity) for a period of 4 days. After drying, the extruded honeycombs and rods were dried in a N ₂ atmosphere at a rate of between 15-25 ° C / hr. preheated to 500 ° C, maintaining the temperature for a period of 4 hours. The honeycombs were cooled to room temperature and then air-cooled at a rate of between 15-25 ° C / hr. heated to a temperature of 500 ° C, the temperature was again maintained for a period of 4 hours. Following this holding, the baking included heating the honeycombs at a rate of 25-50 ° C / hr. to a final temperature of 1100 ° C with the honeycombs held for a final period of 4 hours. The composition of the fired body is in table I indicated.

The resulting bars were used to characterize the mechanical properties such as For example, MOR, CTE and E modulus are used. The thermal shock resistance was according to the following formulas calculated: thermal shock resistance (TSR) = MOR / (E-mod × CTE). The data about the porosity and the average pore size were measured for the honeycomb and were using a conventional mercury intrusion porosimetry technique generated. All these physical properties for the rods and honeycombs are listed in Table I.

Examples 3 to 7

Each example involves careful mixing together of a batch mix as provided in Table I in a Littleford mixer. The zeolite starting material comprised ZSM-5 zeolite with a SiO ₂ / Al ₂ O ₃ ratio of 300 (CBV-3002 from PQ Corporation), the gamma-alumina starting material comprised GL-25 purchased from LaRoche Industries (surface area 260 m ² / g) and the methylcellulose temporary binder included Methocel A4M from Dow Chemical Corporation. One variation included the use of La-stabilized gamma-alumina in Example 7; doped with 4% La ₂ O ₃ and with a surface area of 110 m ² / g. The batch mixture additionally comprised an amount of concentrated silicone resin (6-2230 resin from Dow Corning) dissolved in a dibasic ester solution having the resin / solvent ratio shown in the table; in each example, the amount of resin resulted in the amount of permanent silica binder indicated for the fired composition. Following a treatment with a quantity of oleic acid and / or acetic acid as indicated in the table, the mixed batch was then transferred to a runner and a quantity of water as indicated in Table I was added to the batch and the batch was uniformly plasticized ; It should be noted that each of the weight percents, oil and acetic acids listed in Table I for water are superadditional weight percent based on the final fired composition.

Honeycomb bodies having a wall thickness of about 8 mils and 400 cells / in ² and rods suitable for testing the modulus of rupture (MOR), which had a diameter of 0.793 cm (0.3125 in), were extruded formed by a piston extruder. The green extruded honeycombs and rods of Examples 3-5 and 7 were dried in a manner similar to that for Examples 1 and 2. Example 6 was dried in a dielectric oven for a period of 20 minutes. After drying, the extruded honeycomb and rod green bodies or blanks were fired in a manner similar to that used for Examples 1 and 2, except that the temperature was followed at the second rise in air was not maintained at 500 ° C.

• * Vergleichsbeispiel

The final fired composition, physical and mechanical properties of the extruded zeolite / silica / alumina bodies are shown in Table I. Table I

• * Comparative Example

A review of Table I shows that Examples 3-6 of the invention containing a gamma alumina in the range of 10-50 parts by weight show the required combination of properties. In particular, Examples 3-6 of the present invention exhibit the following combination of properties: (1) a surface area of not less than 170 m ² / g; (2) a MOR of at least 2270 psi; (3) a CTE of less than 2 ppm / ° C; and (4) a calculated thermal shock resistance of at least 1510 ° C.

Referring to Example 7, a zeolite / silica body containing 10 parts by weight of silica, according to Table I, in this sample has less than the desired MOR of 339582 kg / m ² (483 psi). This low strength is likely due to the small amount of silica binder present, especially an amount insufficient to cover the vast surface area of the 90 parts by weight of the combined zeolite and gamma alumina.

It it should be clear that while the present invention in detail with reference to specific illustrative and specific embodiments This has not been limited to this and numerous modifications possible are without departing from the broad spirit and scope of the present invention as he attached in the claims is defined to depart.

Claims (7)

Zeolite body, expressed in weight percent, comprising: 30-70% zeolite having a silica / alumina ratio of at least 300 and a surface area greater than about 250 m ² / g, 15-20% silica binder, and 50% gamma-alumina having a specific surface area greater than 100 m ² / g, the zeolite body having a modulus of rupture of at least 1406138 kg / m ² (2000 psi), a surface area of at least 100 m ² / g, a thermal expansion coefficient of less than about +/- 10 ppm / ° C and a thermal shock resistance of at least 850 ° C. A zeolite body according to claim 1 which has a surface area of at least 170 m ² / g. Zeolite body according to claim 3; the thermal expansion from less than about 5 ppm / ° C shows. Zeolite body according to claim 1, wherein the body a negative thermal expansion less than 5 ppm / ° C having. Zeolite body according to claim 1, wherein the body a thermal stability at a Temperature of up to at least 1000 ° C shows. A zeolite body according to claim 1, which is an extruded honeycomb structure having at least 400 cells / in ² . Zeolite body according to claim 1, wherein the alumina is a stabilizing agent includes, selected from the group consisting of lanthanum oxide, barium oxide, and strontium oxide Yttrium oxide exists.